1. Field of the Invention
The present invention relates to an optical apparatus that changes the optical path of incident light and allows the light to exit.
2. Description of the Related Art
An optical apparatus such as an analog camera (silver salt film camera) and a digital camera is difficult to reduce in the size, especially in the thickness. One of the reasons is the optical viewfinder. Hitherto, various viewfinders have been proposed in order to reduce the overall size or the thickness of cameras.
For example, Japanese Patent Laid-Open No. 2000-338403 discloses a real-image-type viewfinder in which the axis of light entering an objective lens is not parallel to the axis of light exiting an eyepiece lens. According to this related art, the axis of light exiting an eyepiece lens system is tilted with respect to the axis of light entering an objective lens system; an image inverting system is composed of a single roof prism only; and the optical axis is bent in the same plane. Therefore, the mechanism of the viewfinder is simplified and miniaturized.
In addition, Japanese Patent Laid-Open No. 2000-155357 discloses a viewfinder optical system in which a reflecting optical subsystem includes a plurality of free-form reflecting surfaces having power; and at least one of the reflecting surfaces satisfies the following condition:5°<|θ|<25°where θ is an angle of reflection of an axial chief ray with respect to the normal. In this related art, attention is directed to a reflecting surface (hereinafter referred to as independent reflecting surface) that does not function as a transmitting surface and has an unlimited angle of reflection. If the reflecting optical subsystem includes at least one independent reflecting surface, it is possible to reduce the angle of reflection of the independent reflecting surface and consequently reduce the decentration aberration even if the independent reflecting surface has strong power. The reflecting optical subsystem bends the optical path effectively, so reduction in the size of the viewfinder is achieved.
Moreover, Japanese Patent Laid-Open No. 2002-350930 discloses a viewfinder system and an optical apparatus using the same. The viewfinder system includes a first reflecting surface for bending a light path disposed between lenses in an objective lens subsystem; and an image-inverting optical subsystem having a roof reflecting-surface. This viewfinder system achieves a reduction in thickness by bending the optical path at an obtuse angle with a mirror having the first reflecting surface.
The above related arts achieve miniaturization by folding an optical axis of a viewfinder in the same plane. Unlike these, for example, Japanese Patent Laid-Open No. 2002-040361 discloses a display in which an optical axis of a viewfinder is bent in two parallel planes so that an image from a single display element can be seen with both eyes. According to this related art, a three-dimensional optical-path splitting section splits an image from a single display element into light rays for the left eye and light rays for the right eye, and then allows the light rays to enter eyepiece prisms for the left eye and the right eye, respectively. Therefore, an image from a single display element can be led to both eyes without reduction of intensity of the image.
However, the above related arts have the following problems. In the first related art, since the objective lens system and the eyepiece lens system of the viewfinder are arranged in the thickness direction of the camera, reduction in the thickness is difficult. In the second related art, instead of providing an objective lens subsystem having power, the reflecting optical system including reflecting surfaces having power is provided. Therefore, in the case of an optical zoom viewfinder, a lens system for zooming is necessary. The lens system for zooming prevents reduction in the thickness of the optical apparatus such as a camera. In the third related art, in the case of a camera having the viewfinder system, the objective system of the viewfinder extends in the width direction of the camera. Therefore, reduction in the width of the camera is difficult. In the fourth related art, in the case of an optical zoom viewfinder, reduction in the thickness of the optical apparatus such as a camera is prevented, as in the second related art.
As described above, it is difficult to reduce the thickness or the overall size of the optical apparatus, such as a camera, having a viewfinder.